For many years optometrists, ophthalmologists and individuals engaged in eye research have used instruments for studying the eye. Some of these instruments have been used to merely view parts of the eye with or without a contact lens placed thereon; such as, magnifying glasses, slit-lamps and biomicroscopes. Other instruments, commonly called keratometers or ophthalmometers have been used to measure the corneal curvature along the two principal meridians of the eye. The principles of operation of such instruments are well known in the prior art, as shown in U.S. Pat No. 3,791,720 of Walker et al, and the chapter "The Keratometer" published in Clinical Ophthamology, 1976 by applicant Mohrman.
A relatively recent development in ophthalmic instruments has been the development of an instrument that will not only measure the corneal curvatures along the two principal meridians of the eye, but also permits examination of the surface of the cornea with or without a contact lens fitted thereon and the anterior chamber of the eye. One of these instruments merely uses an insertable mask to eliminate the images from all, but one light path. Some disadvantages to this instrument, however, are excessive vignetting and image doubling under certain conditions and an inverted image of the cornea in the viewing mode. Another such instrument embodies two distinct optical systems for the two modes of operation. One optical system provides the measurement of the corneal curvatures along the two principal meridians of the eye and the second optical system provides a magnified image of the surface of the cornea. The mode of operation of the instrument is determined by moving a lever connected to a mask and reflector. In the measuring mode, the image passes through an objective lens, a mask, adjustable optical wedges and through an eyepiece to the user's eye. In the viewing mode, the image is reflected from the optical axis of the measuring system to the optical axis of the viewing system. As light reflected from the cornea progresses through the viewing system, the image is magnified while bypassing the measuring system and returned to the eyepiece of the ophthalmic instrument for viewing. A major disadvantage of this instrument is the expense due to the cost of manufacturing separate optical systems.
In the present invention, an ophthalmic instrument is provided that has an aligning axis for aligning the instrument to the eye and is operable in first and second operating modes. The first operating mode is used to measure the corneal curvature along the two principal meridians of the eye and the second operating mode is used to examine at least the surface of the cornea. In the second operating mode, the surface of the cornea with or without a contact lens fitted thereon and the anterior chamber of the eye may be examined. The instrument includes an eyepiece, an imaging system and reflecting apparatus. The eyepiece is disposed on the aligning axis. The imaging system has an axis displaced from and substantially parallel to the aligning axis and measures the cornea in the first mode and examines the corneal surface in the second mode. The reflecting apparatus displaces an image from the imaging axis to the optical system axis and provides an erect image of the displaced image at the eyepiece in the second mode.